In a known system of the type described, unidirectional current pulses are respectively applied in sequence to the conductors so that the coil produces a measuring signal in the form of a train of induced voltage pulses. A demodulation circuit at the front-end of the evaluator circuit produces an output voltage that corresponds to the envelope of the induced voltage pulses. The evaluator circuit sequentially differentiates this envelope to determine its zero crossing which establishes the location of the coil relative to the conductors.
In another known co-ordinate measuring system, an alternating voltage is applied to the conductors so that a measuring signal in the form of a step-wise variable carrier frequency signal appears in the pick-up coil. A demodulator at the front end of the evaluator circuit demodulates the induced voltage forming an output voltage that corresponds to the envelope of the induced voltage. As in the first mentioned system, the zero-axis crossing of this curve is used to determine the location of the pick-up coil.
An object of the present invention is to provide a coordinate measuring system having an improved evaluator circuit.